Is it your provider request login and password?
You can try add login/password to every url.

The login window has been showing before sometimes, but then i just click "cancel" and i can still watching TV but today it shows everytime i click on a channel and now the channels are not working. I have tried with 2 different providers and it is the same for both.

ps: May be this is access limit. For example no more 2 users in same time.

I have a paid provider. username and password are in the m3u link. I have tried to enter it but it doesnt work. I have tested it on my android phone and it works. This problem started 2 days ago or so. I have been using it with progdvb for a month without problem.

All IPTV services only allow 1 maybe 2 connections with just 1 IP address. Vaders allows 5 connections but only 3 different IP addresses. Maybe you didn't realize the VPN was off when you first loaded the m3u list and was watching it all that time. Turning on the VPN gives you a different IP address which means the m3u list won't work if your IPTV service provider only allows 1 IP address.